This invention relates generally to solid chemical feed systems and, more particularly, to a dual solid chemical feed system which incorporates an automated capability for switching liquid solution containing dissolved solid chemicals from one feed bowl to another when one of the bowls is empty.
The utilization of automatic, solid chemical feed dispensers to dispense chemicals used in industrial and cleaning processes is well known in the art. For industrial applications, such dispenser mechanisms are commonly used to add chemicals to boiler systems or to cooling towers to minimize and/or inhibit corrosion. Automatic dispensers were developed to minimize or eliminate the manual care and attention required to periodically add chemicals to a tank containing the liquid solution. Automatic dispensers are generally placed into two broad categories depending upon the method of controlling the amount of chemicals to be dispensed: (1) time-controlled dispensers; (2) conductivity measurement dispensers.
One example of a method of dispensing a solution that is controlled by conductivity measurements is described in U.S. Pat. No. 4,858,449 issued to Lehn. Lehn discloses an automatic dispenser for dispensing solid chemicals used preferably in cleaning processes. Lehn discloses a dispenser wherein a container holds a quantity of dissolvable solid chemicals which is sprayed with water under pressure to dissolve the chemicals which are ultimately dispensed. The quantity of chemicals dispensed is controlled by measuring the conductivity of the chemical solution.
While automated dispensers have been effective in reducing the amount of manual attention required in maintaining such systems, problems may occur when the chemical in the dispenser container is exhausted. When the solid chemical in the feed container is completely dissolved, the empty container must be manually replaced by a new container filled with a new supply of solid chemicals. If the product is exhausted while the system is unattended, there is potential for the interruption in the chemical treatment of the system. This could occur over a period of hours, or potentially several days, for example, during weekends during which treatment chemicals would not be added to the system. The feed solution created by the dissolution of the solid chemical would not be replenished and would be quickly diluted by the addition of water which is used to maintain a constant level in the dissolution chamber of automatic dispensers. The loss of treatment could result in corrosion and/or deposition of contaminants in a cooling or boiler system, or serious deterioration in the treatment program performance in any system using the automatic solid feed dispenser.
Accordingly, improvements in automatic solid chemical feed or dispenser system is desirable to prevent the loss of chemical treatments which may result in serious damage in industrial systems or the like requiring continuous chemical treatment.
In accordance with a preferred arrangement of the invention, a solid chemical feed system comprises at least two feed bowls, each containing a quantity of solid chemicals that dissolve upon immersion in liquid to form a liquid solution. A sump is provided for receiving liquid solution from each feed bowl, and for containing such liquid solution at a predetermined level. A valve system is coupled to the feed bowls for separately controlling the introduction of liquid to the solid chemicals in each feed bowl. A sensor is supported by the sump in communication with the contained liquid solution for sensing a given, preselected property of the liquid solution, and for generating a signal in response to the detection of such property. A control unit is responsive to such signal for controlling the valve system to alternatingly switch the introduction of liquid from one feed bowl to the other.
In a particular aspect of the invention, there is provided a dual solid chemical feed system comprising two feed bowls, each of which contains a quantity of solid chemicals that dissolve upon immersion in water to form a liquid solution. A source for supplying water to each bowl is provided. A first valve is coupled to the water source for controlling the supply of water to one of said bowls. The first valve is normally maintained in an open position to allow flow of water to one of the bowls. A second valve is coupled to the water source for controlling a supply of water to the other of the bowls. The second valve is maintained in a normally closed position to prevent flow of water to the other bowl. A sump for receiving liquid solution from each of the bowls and for containing liquid solution therein at a predetermined level is provided. A sensor is supported by the sump in communication with liquid solution for sensing the conductivity of the liquid solution and for generating a signal at a predetermined conductivity of the liquid solution. A control unit is responsive to the signal for closing the first valve, thereby preventing flow of water to one of the bowls and for opening the second valve, thereby allowing flow of water to the other of the bowls.
In a further particular aspect of the invention, the feed system includes a third valve coupled to the water source for controlling the introduction of water into the sump. In yet another aspect of the invention, the control unit comprises a time controller for delaying the activation of the first valve and the second valve for a certain period of time after the sensor senses the predetermined conductivity of a liquid solution.
In yet a further particular aspect of the invention, an apparatus is provided for controlling the conductivity of liquid solution in a solid chemical feed system that supplies liquid solution containing dissolved chemicals. The apparatus includes at least one feed bowl containing a quantity of solid chemicals that dissolve upon immersion in water to form a liquid solution. A sump is included for receiving the liquid solution from such at least one bowl and for containing the liquid solution therein at a predetermined level. A water source is provided and a first valve is coupled to the water source for controlling the supply of water to such at least one bowl. A second valve is coupled to the water source for controlling the supply of water to the sump. A sensor is provided in the sump in communication with the liquid solution for sensing the conductivity of the liquid solution, and for generating a signal at a predetermined conductivity of the liquid solution. A control unit is included which is responsive to the sensor signal for opening the first valve and closing the second valve to thereby supply water to the feed bowl when the conductivity is below the predetermined conductivity, and for closing the first valve and opening the second valve to thereby supply water to the sump when the conductivity is above the predetermined conductivity. The apparatus for controlling the conductivity of the liquid solution is also used in a solid chemical feed system comprising two or more feed bowls. When the chemicals in one of the feed bowls is depleted, the control unit may alternatively switch between supplying fresh water directly from the water source to the sump or through the one bowl wherein the chemicals are depleted to lower the conductivity of the liquid solution in the sump.